This invention is directed to a control system for the production of a product. The control system of this invention has the capability of rapid information processing and display, minimizing production cycle time, efficiently allocating resources, and minimizing excess costs.
In the production of products, the work effort is a sequence of operations. The proper control of these operations is as important to the efficient transformation of the product from its initial state into its finished state as the individual operations themselves. Just as an improvement in each operation can improve the production rate, an improvement in the control of the production process can produce a similar reduction in total cost and the elapsed time of production.
For example, in U.S. Pat. No. 3,703,725, the method of control uses a computer to balance work flows in a manufacturing process. In U.S. Pat. No. 3,845,286, a control system sequences semiconductor wafers through a number of workstations. In U.S. Pat. No. 4,027,246, a central computer controls the transfer and processing of semiconductor wafers. Although these inventions teach methods for manufacturing control, and an improvement in efficiency, they do not teach a method for maximizing manufacturing efficiency and thereby minimize manufacturing time and cost. In the production of any product, the costs of idle waiting time, penalties due to late delivery, unjustified expediting costs, and the costs of excess inventories must be minimized.
One system that has addressed this problem is the Critical Path Method (CPM), in which a network of activities is created that represents the sequence of operations and the interdependencies of the operations in the particular production process. A variation on this basic method is Project Evaluation and Review Technique (PERT) which uses multiple estimates of time durations to provide a probabilistic output. These systems are available as computer software. To use these systems, the networks are analyzed to fine the critical path; i.e., the path that is, in effect the longest duration, and which determines the final completion date.
A major problem of these systems is that critical items that lie on the critical path must be searched serially; each requiring a computer run, at a considerable expense in time and money on large projects. Also, potentially critical items are not identified. Further, for every change in the availability date of any item, the impact on the final completion date can only be assessed by another computer run. Although valuable, these systems do not provide an easy and timely visability into the critical items and their degree of impact. Also, these systems do not offer a means to balance resources in order to minimize the time and cost of a project.